Resonator removed.

[svxistentialist]

In the tyre/exhaust shop today. Had 4wheel laser tracking done on the 4 new tyres. Car running and handling very very well.

I asked them to weld up the heat shields on the cats. Was having a nuisance buzzing and fizzling under load at c. 2000rpm. Totally annoying. They discovered the noise was mainly from the centre box, a resonator I think it's called. Had them cut it out, and replaced by a straight pipe.

It's not much noisier on tickover, or under hard acceleration. However, I find it a good deal boomier at between 1500 and 2000 rpm, where the engine likes to stay.

Has anyone else done this? Any known drawbacks?

Joe

[CDG]

I believe its quite common for these resonators to be removed with no ill effects. Mine was removed when I bought it.

[svxistentialist]

I just ran a search, and realised there is an existing thread on this.

Harvey, who generally knows his onions, reckons the straight pipe will lead to lost power higher up.

Does this mean I can expect better torque lower down with the see-saw effect??

Might pay off for the extra boom.

Joe

I had my resonator removed not too long ago, and have noticed the same effect. 1800 - 2000 RPM seems to be the key for me, sounding off just a slightly lower/boomy-er tone. Idle doesn't sound quite as pretty as it used to, though. Just slightly bubbly now...

As for the power loss, I haven't been able to physically notice anything. Of course, the seat-of-the-pants opinion isn't scientific... I just didn't feel any kind of change after the removal.

The damn buzzing in my heatshields came back though

[svxistentialist]

That's exactly where mine is making a boomy noise.

Notice it most when the window is open, passing walls etc.

Overall the noise is not excessively high, but I prefer it original, and will buy a new box to put in there. You can hear the sound over the stereo at low revs, and the sound will become tiresome, particularly I expect in city driving.

joe

[oab_au]

Originally posted by svxistentialist
I just ran a search, and realised there is an existing thread on this.

Harvey, who generally knows his onions, reckons the straight pipe will lead to lost power higher up.

Does this mean I can expect better torque lower down with the see-saw effect??

Might pay off for the extra boom.

Joe

No Joe, no tradeoff.
The pressure wave that flows down the pipe from the cylinder, will hold pressure in the pipe right back to the cylinder, till it reaches a point where it can expand and drop the pressure down.

This gas pressure travels at the same speed (300 to 700ft/sec) regardless of engine speed. At low RPMs there is time for the wave to reach the end of the pipe and drop pressure for the cylinder to scavage. At higher RPMs there is not enought time for this to happen, to scavage the cylinder, so power is degraded.

To fix this situtation, we would need a shorter exhaust pipe. To simulate this we fit an expansion chamber/resonator, up closer to the cylinder, so that the pressure wave can expand into this, like it was the end of the pipe, and drop pressure in time for the cylinder to scavage.

That is why it is fitted. removing it will drop power at higher RPMs, like when you hit POWER mode to overtake that line of cars, that potent top end surge from 4000 on will be lacking.

A long straight pipe may suit a low reving bent 8, but to hold power up to 6800 takes more technology in the exhaust design. yes fit another, does not have to be a Subaru replacement, the bigger the better.

Harvey.

[svxistentialist]

Thanks for the technical slant Harvey.

I will be putting back a/the resonator. I absolutely dread aftermarket noise boxes anyway. My view is that all cars should sound like a Toyota Prius on tickover, i.e. completely silent, should be capable of 200 mph and do 0-100-0 in about 10, 12 seconds. All this without Days of Thunder.

Did you read Sonar's post about cutting open the box, brazing up a loose baffle and opening some extra holes before refitting it?

Even though it is now a little boomy, it's preferable to the fizzle and rattle that went before. Car no longer sounds like something is going to fall off it.

Joe

[CDG]

Excellent point Harvey, I may just go get something to fill that whole.
So if I just remove the pipe, therefore opening my exhaust at the resonator part, then my top end should be better?
However somewhat unbearable in noise
I do know this may effect bottom end too.

I did some of this fun tuning on a old Mini Cooper S 1275cc engine. And providing an expansion chamber at the right distance from the heads provided us the ability to tune the engine to peek performance at the right RPM.
This is the core concideration for all 2 stroke engines, tuned exhaust makes a big difference.
But one needs to tune 3 perameters, bottom end, tops end, and noise. Plus emissions I guess is a 4th.

[oab_au]

Originally posted by CDG
Excellent point Harvey, I may just go get something to fill that whole.
So if I just remove the pipe, therefore opening my exhaust at the resonator part, then my top end should be better?
However somewhat unbearable in noise
I do know this may effect bottom end too.

I did some of this fun tuning on a old Mini Cooper S 1275cc engine. And providing an expansion chamber at the right distance from the heads provided us the ability to tune the engine to peek performance at the right RPM.
This is the core concideration for all 2 stroke engines, tuned exhaust makes a big difference.
But one needs to tune 3 perameters, bottom end, tops end, and noise. Plus emissions I guess is a 4th.

Yes Chris you don't see too any race sedans that run a tail pipe out the back. They just run the short pipe out under the front doors, spiting flame and noise.

Tuning a Mini you brave man, great wet weather distrubitor, jumping gear shift, and no booster for the disk brakes. Not to mention the torque steer that takes you to the wrong side of the corner.

Harvey.

[CDG]

Distibutor was replaced with and sweet little electronic goodie, worked very well, the Cooper front end is much wider, torque steer wasn't that bad, Jumping gear shift, you know it, Used a bungie cord for hiway driving, brakes were better on the cooper. Unfortunately the engine only lastest about 3500miles before it blew out the trany(Trany sits in the oil pan, uses engine oil for its lubricant/destruction ) It was one scary fast little 1200lb car, nothing could beat it off the line but a fast bike. Had 4 x 38mm carbs, austin marina head, straight thru tuned Gary Wolfe custom Header(I actually made it, but it was his shop, and advice) Magically tuned exhaust, 2.5 inch in, 2 inch out, glass pack spark arrestor. I was ready to add the turbo charger when the trany went pop. Car was dyno'd at 130hp, may not sound like much, but we expect it should have been higher if not for the bad tires. remember, 1200lbs just over with both 5.5 gallon tanks filled.

[oab_au]

Good one Chris, yes I know them well, but not for fun times. I worked on too many of them back then.

Harvey.

[CDG]

When the trany gave out, I sold the engine/trany for $500, and cut the car in 2 with a cutting torch and turfed it into a dumpster, It took about 20 minutes, my boss was not impressed.